Re: [PATCH 5/6] x86/microcode/intel_staging: Support mailbox data transfer

[Chang S. Bae]

On 2/18/2025 12:54 PM, Dave Hansen wrote:
> BTW, is this kind of read/write normal for MMIO reads? It looks really
> goofy to me, but I don't deal with devices much.

Yeah, looking at some device code, functions like memcpy_toio() and 
__iowrite*_copy() seem to assume sufficient MMIO space to copy data from 
kernel memory. I also noticed that some other mailbox code calls back 
one of these functions.

So, I think your assessment is correct:

  > To me, it's much more akin to talking over a serial port than how I
  > think of devices attached via MMIO.

Certainly, this staging mailbox looks somewhat similar to a serial port. 
I suspect the staging portion is quite resource-limited. That appears to 
be one of key characteristics of this interface, which I should 
highlight more comprehensively.

Thanks,
Chang